Electric arc cutting machine



July 14, 1936. STROBEL Re. 20,035

' v ELECTRIC ARC CUTTING MACHINE Original Filed May 9, 1932 3Sheets-Sheet l '3 28 M zo 9 55 1.3. V g 42 -21 27 J9 7 as n I 4 1 Z A/3" L@ I x 67 Inventor M W v July 14, 1936. K. STROBEL ELECTRIC ARCcuwwme MACHINE Original Filed May 9, 1932 3 Shets-$heet 2 Inventor July14, 1936. K. STROBEL rangc'rmc ARC CUTTING MACHINE Original Filed llay1952 3 Sheets-Sheet 3 Inwentar WMW Rama-a July 14, "1936 UNITED STATES20,035 Emc'raio l no cu'r'rmo MACHINE Karl Strobe, Whlttier, am, StrobelCorporation, Puente,

tion of California Original so. 2,007,225, dated May 9, 1932.

1936, Serial No; 81,693

No. 610,086, issue May 25,

assignor to Karl CaliL, a corpora- July 9, 1935, Serial Applicationforre- 14 Claims." (c1. 219-1) the same. Such prior devices, howevergcannotbe employed to make a relatively narrow cut,

' since it is necessary that the entire metal surrounding the cut shallbe heated to the ignition point and the result is a separation betweenthe cut sections of material Moreover, the employment of such methodsfor cutting requires bringingthe temperature of the metal up to theignition point before the burning or cutting effect begins and the metalis therefore so heated that for a considerable distance on each side ofthe actual cut the metal is overheated. In the ;case of cutting hardenedor tempered metals, such overheating causes the metal on each side ofthe cut to become soft, or to become crystallized, depending upon thecharacter of the metal which is out.

It is, therefore, an object of my invention to provide a device. for.cutting metals by means of an electric arc in which the width of the cutisonly asgreat as the thickness of the electrode employed to make thecut. Another object of the invention-is to provide a device for cuttingmetals with an electric arc in which no oxidizing agent is required. I

Another object of my invention is to provide a device for cutting metalswith an electric arc in which the heating of the metal is confined to anarrow band substantially equal to the thickness of the electrodeemployed, and in which the metal on each tially cold during the cuttingoperation.

Another object of my invention is to provide a device for cutting metalswith an electric arc in which the finished cut presents a smooth lineedge having the same appearance as though the metal had been cut by acontact saw. Another object of my invention is to provide a device-forcutting metals with an electric arc in which the metal to be cutmay beharder than the material ofthe electrodeemployed for-the cutting.

Another object of my invention is to provide a device for cutting metalswith an electric arc in which the only mechanical contact between thecutting electrode and the workpiece to be cut is .a momentary 1. ontactnecessary to start the arc.

Other objects and advantages will be apparent from a study the followingspecifications readin connection with the ac ompanying drawings, whereinthe metal while so heated to consume I rough, erratic line of side ofthe cut remains substan-- Figure 1 15 a perspective view of an arccuttingmachine constructed in accordance with my ln-' vention;

-.Figure 2 is a vertical sectional" view, taken through the electrodeand work table illustrating the manner of mounting-the electrode and themanner of supplying current thereto;

Figure 3 is a horizontalsectional along line IIIIII of Figure 2;

Figure i is'a diagrammatic view of the wiring view, taken a Re. 20,035"PATENT 7OFFICE system employed in connection with my are cut--' tingmachine; and

. Figure 5 is a diagrammatic view illustrating the action of the arebetween the electrode and the workpiece to be cut. I

Referring to the drawings, I have illustrated my electric are cuttingmachine as comprising a suitable work-table I having a top 2 supportedupon a plurality of le gs,3 to elevate the table toany suitable height.The table top 2 consti tutes the support for the metal which is to becut and which may be clamped in place thereon by means of any, suitableclamping device, such as a vise structure 4 mounted upon the table top.The table top is provided with a suitable slot 5 extending therethroughover which the workpiece 6, or section of metal to be cut, may

extend. I

The cutting electrode is illustrated as comprising a circular disk 1,similar in construction to the circular saws now employed for mechanicalcontact sawing, the disk being mounted upon a' suitable rotatable shaft8 permitting the disk 1 to be rotated relative to the table I.

, The disk 1 is illustrated'as .being rotatable by any suitable sourceof power, such as an electric motor 9, the armature of which isconnected to the shaft 8 either directly or through gearing III in orderto produce the desired speed of rotation of the disk 1. Since the disk 1is to constitute oneof the electrodes employed for producing theelectric arc, it is desirable to insulate the disk 1 from its shaft 8and from the motor 9, and for this purpose I have illustrated the shaftas being 7 provided with a suitable radial flange II against which aninsulating disk or cup I! may bear, presenting a plane surface' againstwhich one side of the disk 1 may be clamped. An insulating bushing 13may be interposed betweenthe bore ll through the center of the disk 1and the shaft 8, while a second cup-like washer I5 may be interposedbetween the disk 1 and the clamp- 7 lug nut l6 employed to retain thedisk upon the shaft I." In order to conduct electric current to the disk1 a washer or ring [1 of suitable conducting material may beinterposed'between the insulating washer l5 and the side of the plate ordisk 1.

The disk is arranged to be operated by a motor 9 at a relatively highspeed, and a guard ll may of slides 35 and 38 engaging a track .31formed '1. The guardis preferably formed of nonmag:

netic material to prevent creation of undesired magnetic flelds aroundthe electrode.

' The guard l8 may be employed for mounting suitable electricalconducting devices supplying current to the disk I, as, for example, bymounting a relatively large sheet 2| of insulating material upon oneside of the housing or guard 18, the

' material of the guard l8 being cut .away' adjacent the inside surfaceof the 'plate or sheet of insulating material 2|, as is indicated at 22.A brush mounting 29 is illustrated as being secured to the plate 2|,comprising a cylindrical bushing having a bore- 24extending therethroughand through the plate 2| to mount a suitable metallic brush 25 pressedinto contact withthe conducting ring .ll

under the influence of a suitable compression spring 29. The pressureexerted by thespring 29 may be suitably adjusted by means of a plug 21threaded into the outer end of the brush mounting bushing 23.

Hence current supplied to the brush mounting. bushing 29-will beconducted through the disk 1,

while it is being rotated by the motor 9', so' that an arc may be drawnbetween a workpiece laid upon the table-top 2 and the rotating electrode1.-

By referring particularly to Figures 1 and 2, it will be observed thatthe motor 9 is mounted upon a suitable mounting plate 28, illustrated asbeing formed from a section of conventional channel iron to which issecured a pair of vertically extending plates 29 and 90. The plate 29 isillustrated as having secured thereto a pair of runners or slides 3| and92 to engage above and below a track 93. The track 33is preferablyformed from a section of conventional I-beam 34 with the edgesi'of theflanges thereof beveled and machined to provide upper and lower trackson which the slides 9| and 32'may operate. The plate 39 isalso'illustrated as being provided with a pair upon the other flange ofthe I-beam. This construction forms amounting for the motorwhich permitsthe same to be moved longitudinally of the r-beam ,butwhich supports themotor rigidly in a vertical direction. An outstanding boss 99 maybeformed upon the plate 90 to constitute a nut engaging a threaded screw29 by which the-motor and its mounting may be moved hori- ,tontallyalong the I-beam track 94. The I-beamtrack is, illustratedas beingslidably supported upon a pair ,of uprights 49 and 4| so that the I-beamwith its motor and disk may be recipr beam 34. The opposite end of theI-beammay be 9 as is illustrated herein upon a' slide 45 engaging'rocated his vertical" direction. The upright 40 is illustrated ascomprising a frameat the top mounting for the I-bea'm 34., a The screw42 may be provided with a suitable operating handle 44 permitting thescrewto be readily manipulated to elevate or' lower the I-suitablethreaded nut structure 42 forming a nut mounted in a similarmanner or may bemounted the upright 4|. In order to cause the slide 45to ,be elevated in accordance with the elevation of the nut 49, asuitable counterweight 44 may be connected by means of a flexible chainor cable 41 forward end thereof so that manipulation of the a handle 49willcause the motor and its disk to be molten particles of the metal,and bottom of which a vertical feeding screw 42 may be journaled, thefeeding screw engaging a and. the workpiece is actually to the I-beam34', the chain or cable passing over a suitable pulley 49 supported uponthe upright 4 I.

I "If desired, the upright 4| may be formed ofia tubular post with thecounterweight slidable within the same. Thus the manipulation of the-single handle 44 may be employed, to elevate or I lower the motor 9 andthe disk I. The lateral feed screw 39 may be manipulated by means of asuitable handle 49 secured to the screw at the moved horizontally alongthe I-.beam track. Thus the disk may be moved to any desired po-. sitionin the vertical plane in which it rotates, this plane being aligned withthe plane of the 15 slot 5 of the work-table so that the lowermostportion of the disk may pass below the level of P :the table-top 2.

It will be'observed" that the disk 1 constitutes an electrode having arelatively narrow elongated 20 edge 50, which, upon rotation of the diskby the motor, will cause the edge'of thedisk to pass continuouslyin thesame direction past the work-. piece upon the table. Thus an arc isdrawn be- .tween the edge of the electrode'and' the nearest 25 point ofthe workpiece. Thearc so drawn will heat a section of the metal of theworkpiece'immediately adjacent the electrode to the point of fusion, thespeed of the movementof the edge of the electrode relative to theworkpiece causing 30 fused particles of the, workpiece to be drawn inthe-'direotionof the movementof the electrode edge so that as soon asminute particles of the .workpiece are melted, they" are immediatelyever, will're'main between the workpiece and the nearest'point oftheedge of the electrode so that as eachparticle' is removed the arccontinues to melt the next portion of the workpiece material.

By referring particularly to Figure 5, it will be observed that if theelectrode "I is rotating in the direction indicated by the arrow, themechanical contact of the electrode edge ill with the extreme edge SI ofthe workpiece 6 will cause an arc to be started between the electrodeedge 50 and the workpiece'i. As the arc melts the metal, the rotation ofthe electrode edge will cause the particles to be drawn away from theworkpiece along a line tangent to the edge 59 of the electrode I, as isindicated at 52.

By operating the feed screw 99, the electrode is drawn toward andthrough the workpiece in a direction transverse to the rotation oftheedge 59 of the electrode, thus permitting the arc to v penetrate furtherthrough the workpiece until the'edge ofthe electrode has passedcompletely through the workpiece, severing the same into two separateparts. J In order to assist the throwing out of the the edge 50 of the 6electrode may be provided with a plurality of serrations .or -teeth 53similar to the teeth employed upon conventional mechanical contact saws,so that the are between the electrode edge I drawn from the points ofthe teeth. g 7

While the theory of the melting and'removal of the particles is notfully 'understood, it has been'observed in actual practice that theemployment of teeth of the shape shown produces the most desirableresults, apparently the combined tendency of the arc to follow thetrailing surfaces the'cup. Also the formation of the teeth is pref-.

erably like that of mechanical contact sa'ws in that the edge of the sawis swedged out to provide a greater width at the outer edge of the teeththan the width of the electrode diskat points closer to its center. Thusthe are which is drawn from the extreme edgeof the teeth will be su1-'i'iciently wide to insure removal of the metal to form a cut, thesidesoi which clear the sides of the electrode disk.

In view of the fact that the cutting operation is formed entirely by thearc, and not by mechanical contact betweenthe teeth of the electrodeandthe workpiece, any metal, irrespective of its hardness, may besuccessfully outwith an electrode which is formed of much softer metal.The primary essential characteristic of the material from whichtheelectrode is formed is that it must be sufiiciently tough to stand upunder rapid rotation and must. be sufliciently rigid to maintain allparts of the edge in the same vertical plane while rotating. I haveemployed a relatively soft steel saw, such as may be used for woodcutting, and with such saw I have succeede'd in cutting metals havingsubstantially diamond hardness. An interesting phenomenon is that withmy cutting device the' electrode 1 does not heat up to any appreciableextent duriug the cutting operation, and, in fact, imme diately afterthe termination of a cut, the edge of the electrode may be readilygrasped with the fingers and shows no substantial increase intemperature above the temperature of the surrounding atmosphere.

' trode tostart the are or by laying a strip of carbon or other softconducting .material immediately in advance of theworkpiece so that thearc may be originally drawn between this mate- .rial and the electrodeinstead oi initially drawing they are by contact with the workpiece.Howstanta'neous that after many cuts of, extremely hard material havebeen made by the saw, no ap-,

preciable dulling of the tool occurs, indicating that the inttantaneousmechanical contact was of such short duration that there was little orno effective mechanical contact maintained.

.As the electrode enters the cut in the workpiece there is a tendencyfor the arc to travel inwardly along the sides of the electrode which,would tend to heat the electrode and tend to.

burn away metal along the sides of theeut. To avoid this a magneticfieldmay be created in the electrode disk which will tend to drive thearc radially from the disk and will tend to confine the arc to the edge'only of the electrode.

this purpose, any suitable means for creating a magnetic field in theelectrode may be employed, though the embodiment of my inventionemploying a disk electrode, as shown herein, I prefor to create themagnetic field by means of a coil 54 through which'the electrodeprojects.

By. referring particularlyto Figures 2 and 3, it

will be observed that the coil 54 is formed by 'a continuous length ofconducting material wound in the form of a tapered helix, the taper ofwhich is directed toward the edge of the electrode; That is, the coil-54may extend from a suitable ter-.

minal 55 around the interior of the guard l8 in The only mechanicalcontact I which is made between the electrode and the For -"in' linewith the edge of the electrode.

the electrode 1 As the coil spaced relation to continues in the form ofa second turn about the ard I8.

I find that the best resultsare achieved when the line drawn through thecenters ofthe conductors'on one side of the electrode and a line drawnthrough the centers of the conductors on the other, side of theelectrode intersect each other substantially at the edge 50 of theelectrode. Such condition is illustrated by the dotted line arrows 56and 51 inFigure 2. Thus the electrode is in effect a magnet which tendsto blow the arc transversely to the direction'of constant move-' mentbetween the edge" ot the electrode and the work-piece and any tendencyfor the are to creep back along the sides of the electrode iscounteracted.

For simplicity in construction, the coil il'may be formed from a bar orconducting material having a. relatively great cross-sectional areasuilicient to carry the current employed in the arc, and this coil maybeconnected in series relation with the electrode 1 so that all of thecurrent which passes through the arc will also pass through the coil,thereby creating a blowing or driving force proportional at all times tothe amount of the current employed in the arc. Thus the coil extends, asshown in Figure 3, from the terminal .55 and around the electrode 1 to asecond terminal 59 which is bridged by means of a strap-50 to the brushmounting] bushing 23, so that current supplied to the electrode willfirst pass through the coil and then passto the electrode.

In view of the fact that at the instant of drawing an arc asubstantially short circuit is created,

it is desirable that some current limiting device be interposed betweena source of supply and the electrode. ever, inpractice this initialcontact is so in- By referring 'to Figure 4, it will be observed that atypical wiring system which may be employed may comprise connection ofthe electrode 1 to a suitable source of supply, through the conductor5l,-an arc control switch 52, a current limiting resistance 531mm whicha conductor 54 extends to the terminal 55. Thence the circuit extendsthrough the coil 54, through the terminal 59, bridge 50, brush 25,contact washeror ring II to the electrode disk 'I. The circuit iscompleted through the workpiece 6 and table top 1 which may be connectedin any suitable manner, as by conductor 5'l,'to the opposite terminal ofa source of electric current.

While I prefer to use supply for the arc, alternatingcurrent maybeemployed with substantially equally good results.

i It will be observed that by confining thearc to the edge of theelectrode, and by causing the arc to be projected outwardlyfrom theelectrode edge in a direction substantially transverse to the movementbetween the electrode edge and the workpiece, the only portion of theworkpiece ,tm-

be out which will be heated will be that directly Thus no direct currentas the substantial heating of the metal on either side, of

curs beyond 1 m. m. on either side of the cut. Hence tempered materials,suchas springs .and-

the like, may be readily'cut with my saw without drawing the temper fromthe material to a-distance greater than 1 m. m. on either side of thecut. Also, the appearance of the sides of the cut performed by my arecutting device is smooth and straight, the appearance being identicalwith desiredlength. I

The automatic control of the feeding of the that of a cut made bymechanical contact saws, such as hack saws or what is known as thetriotion saw.

While the cutting operation may be performed with any desired speed 0!movement of the-edge or the electrode relative to the workpiece, thebest results are obtained when there .is a relatively high speed ofmovement between these. members, the greater the speed of movement, the

being that the electrode must have an elongated relatively narrcw'edgefrom which the arc may be drawn and which edge may be driven past thematerial or workpiece to be cut at a relatively high speed.

If desired, thefeeding movement of the disk toward and through theworkpiece to 'be cut may be. automatically controlled so thatthearc'between the workpiece may be maintained at any electrode may beaccomplished in any desired manner, suchqas that illustrated in Figure4,

wherein the feed screw 39, which controls the lateral movement of theelectrode I and its motor 9, may be connected to' a suitable drivingmotor 10, the armature "ll of which may be connected across the arc, asby connecting one terminal of the armature to conductor 64 whichsupplies current to the electrode I, and connect ing the other terminalof the armature II to the workpiece. The-field winding 12 of the motorI0 is connected to any suitable constant source of energy so that as thearc'length increases more current will be supplied to the'armature Ii01' the motor and it will rotate the'screw 39 to feed the electrodetoward the workpiece, while, as the 'arclength decreases less currentwill be supplied to the armature II, and the feeding movement 01 theelectrode will be reduced.

While I have shown and described the pre-' Ierred embodiment of myinvention, 1 do not'desire to be limited to .any of the details' shown Iclaim: I 1. in a device for cutting metals with anelecexcept as definedin the appended claims. 7

} trio arc, anelectrode having an elongated edge,

means for applying electric 'potential ,between said electrode and aworkpiece to be cut to pro duce an arc th'erebetween, .teeth i ormedupon said elongated edge having their extreme outer edges ofgreaterwidth than the remainder of said electrode, means for producingcontinuous unidirectional movement between said electrode edge and saidworkpiece,.and means for moving the edge of said electrode toward andthrough said workpiece in a direction transverse 'to unidirectionalmovement.

2. m a device torcutting metals with a. elec-Q tric are, an electrodehaving an endless'elon gated iedge, means for applying electricpotential between said electrode and a workpiece to be cut to prod'uceanarc therebetween, teeth rm upon said elongated edge having theirextreme" outer edges of greater width than the remainder of saidelectrode, means Ior'producing a continu-' ous unidirectional movementbetween said electrode" edge and said workpiece,'and means for movingthe edge of said electrode toward and throughsaidworkpiece in adirection transverse to said'unidirectional movement. v

3. .In a-device for cutting metals with an elec trlc arc, an electrodehaving an elongated toothed edge, the peripheral edge of said elec'-"'trode being formed of greater width than the remainder of saidelectrodeto confinefan arc 'to the front edge or said teeth, meansiorapplying electric potential between said electrode and a workpiece tobecut to produce an are therebetween, means for producing continuousunidirectional movement between said electrode edge and said workpiece,-and means for moving the edge-oi said electrode toward andthroughsaid-workpiece in a direction transverse tosaid unidirectional movement.V

4. In a device for'cutting metals with an electric arc, an electrodehaving anelongated edge. teeth formed upon said elongated edge having.theirextreme outer edges or greater width than the remainder of'saidelectrode, means for applying electric potential between saidelectrode and ,a workpie'ceto be cut to produce an are therebetween,i'or producing continuous unidirectional movement between saidelectrodej edge and said workpiece, means for' moving the edge of saidelectrode toward and through said workpiece in adirection transverse tosaid unidirectional-movement, and a coil in circuit with'said electrodeand disposed relative to said electrode to create a magnetic fieldtherein. one pole'ot which lies at the center of said electrode and theother poleof which lies at the peripheral edge of saidelectlode forconfining the arc to the surface of the edge of said electrode.

5. In a device .for cutting metals with an electric arc, an electrodehaving an elongated edge,

teeth formed uponsaid elongated edge having their extreme outer edges oigreater width than the remainder of said electrode, means forapplying-electric potential between said electrode and a workpiece to becut to produce an arc therebetween, means. for producing continuousunidirectional movement between said electrode edge and said workpiece,means for moving the edge .of said electrode toward and through said Iworkpiece in a direction transverse to said unidi rectional-movement,'and. a coil through which I said electrode projects forcreating a magnetic field in said electrode, one pole at which lies at,the center of said electrode and the other pole of which lies at theperiph ral edge or said electrode for confining the ar'c to the edge or.said electrode. v J '6. In a device for cutting metals with an elec-''tric arc. an electro'de'h'aving'an el'ongated edge,

teeth formed upon said elongated edge having their extrem'eouter edgesof greater width than the remainder of said electrode, means i'orapplying electric potential between said electrode and a workpieceto'be'cut toproducepan arc therebetween, means for" producing continuousunidirectional movement between said electrode edge and said workpiece,means for moving the edge of said electrode toward and through saidworkpiece in a direction transverse to said unidirectional movement, anda coil through which the edge of said electrode projects, said coilbeing formed of a helix tapering toward the edge of said electrode forcreating a magnetic field confining the arc to the edge of saidelectrode.

'7. In a device for cutting metals with an electric are, an electrodehaving an elongated edge having a plurality of saw-like teeth formedthereon, and having the outer edge of said teeth of greater width thanthe remainder of said electrode and confining an arc to the outer edgeof said teeth, means for applying electric potential between saidelectrode and a workpiece to be cut to produce an arc therebetween,means for producing a continuous unidirectional movement between saidelectrode edge and said workpiece, and means for moving the edge of saidelectrode toward and through said workpiece in a direction transverse tosaid unidirectional movement.

8. In a device for cutting metals with an electric are, a diskelectrode, teeth formed'upon the peripheral edge of said disc havingtheir extreme outer edges of greater width than the remainder of saidelectrode, means for rotating said disk electrode, means for feedingsaid electrode toward and through said workpiece in a directiontransverse to the axis of rotation of said electrode, and means forapplying electric potential between said disk electrode and theworkpiece to be cut to produce an arc between the edge of said electrodeand said workpiece.

9. In a device for cutting metals with an electric arc, a discelectrode, teeth formed upon the peripheral edge of said disc havingtheir extreme outer edges of greater width than the remainder of saidelectrode, means for rotating said disc electrode, means for feedingsaid electrode toward and through said workpiece in a directiontransverse to the axis of rotation of said electrode, and means forapplying electric potential between said disc electrode and theworkpiece to be cut, and means for creating a magnetic field in saidelectrode with the center of said disc constituting one pole of a magnetand the edge of the disc constituting the other pole of the magnet.

10. In a device for cutting metals with an electric are, an electrodehaving an elongated peripheral edge, teeth formed upon and extend- 55ing outwardly from said edge, means for applylog electrical potentialbetween said electrode and a workpiece to be cut-to produce an arctherebetween, means for producing continuous unidirectional movementbetween said electrode edge and said workpiece, means for moving theedge 01' said electrode toward and through said workpiece in a directiontransverse to said unidirectional movement, and a coil in circuit withsaid electrode and through which said electrode projects for creating amagnetic field in'said electrode, one pole of which lies at theperipheral edge of said electrode and the other pole of which lieswithin said electrode in spaced relation to said edge.

11. In a device for-cutting metals with an electric arc, an electrodehaving an elongated peripheral edge, teeth formed upon and extendingoutwardly .from said edge, means for applying electrical potentialbetween said electrode and a workpiece to be out to produce an aretherebetween, means for producing continuous unidirectional movementbetween said electrode edge and said workpiece, means for moving theedge of said electrode toward and through said workpiece in a directiontransverse to said unidirectional movement, and a coil in circuitwith'said electrode and through which said electrode projects forcreating a magnetic -ileld in said electrode, one pole of which lies atthe peripheral edge of said electrode and the other'pole of which lieswithin said electrode in spaced relation to said edge, said coil beingformed of a helix of wire said helix tapering toward the edge of saidelectrode.

12. In a device for cutting metals with an electric arc,an electrodehaving .an elongated peripheral edge, teeth formed upon and extendingoutwardly from said edge, means for applying electrical potentialbetween said electrode and a workpiece to be cut to produce an arctherebetween, means for producing continuous unidirectional movementbetween said electrode edge and said workpiece, means for moving theedge of said electrode toward and through said workpiece in a directiontransverse to said unidirectional movement, and a coil in series circuitwith said electrode and through which said electrode projects forcreating a magnetic field in said electrode, one pole of which lies atthe peripheral edge of said electrode and the other pole of which lieswithin said electrode and in spaced relation to said edge. I

13. In a device for cutting metals with an electric are, a discelectrode, teeth formed upon the peripheral edge of said disc andextending radi-- ally therefrom, means for rotating said disc electrode,means for feeding said electrode toward and through a workpiece in adirection transverse to the axis of rotation of said electrode, meansfor applying electric potential between said disc electrode and saidworkpiece to be cut to produce an are between theedge of said electrodeand said workpiece and a coil disposed about said electrode and throughwhich the edge of said electrode projects, connected in series circuitrelation with said disc electrode and said workpiece for confining thearc to the peripheral edge of said disc electrode. 1

14. In a device for cutting metals with an electric arc, a'discelectrode, teeth formed upon the peripheral edge of said disc andextending radially therefrom, means for rotating said disc electrode,means for feeding said electrode toward and through a workpiece in adirection transverse to the axis of rotation of said electrode, meansfor applying electric potential between said disc electrode and saidworkpiece to be cut 60 to produce anarc between the edge of saidelectrode and said workpiece, and a coil disposed about said electrodeand through which the edge of said electrode projects, connected inseries circuit relation with said disc electrode and said 5 workpiecefor confining the arc' to the peripheral edge of said disc electrode,said coil being formed of a helix of wire surrounding the saidelectrode, said helix tapering toward the edge of said disc electrode. 7

KARL STROBEL.

